For example, a prior signal processor of a pulse encoder comprises photodiodes and resistors, and when light is made incident onto the photodiodes, a current flows through the photodiodes in response to a strength of the light, and voltage caused by the flow of current through the photodiodes at both ends of the resistors, are picked up as the output signals.
Note, recently a technique for improving a resolution of a pulse encoder has been studied and developed by processing the photoelectrically converted output signals. In the prior art, a signal processor of the pulse encoder for improving the resolution of the pulse encoder such as the above described device has been proposed which, for example, comprises four differential amplifiers and outputs signals having a phase difference of 45 degrees from four output signals having a phase difference of 90 degrees.
However, in the signal processor of the pulse encoder according to the prior art, one photoelectrically converted output signal is directly applied to the input terminals of a plurality of differential amplifiers, and each of the differential amplifiers has a hysteresis resistor connected in parallel between the input terminal and an output terminal thereof. Consequently, the photoelectrically converted output signal applied to the input terminals of the differential amplifiers are affected by the output terminals of the differential amplifiers through hysteresis resistors, so that the four signals processed by the differential amplifiers do not have a correct phase difference of 45 degrees.